# Lesson Worksheet: Hydroelectric Power Physics

In this worksheet, we will practice describing the advantages and disadvantages of generating electricity from hydroelectric dams.

Q1:

A hydroelectric dam has 28 turbines, each of which has a maximum power output of 9 MW. The turbines are several decades old, however, and are to be replaced with newer turbines, which are more efficient and have a higher maximum output power. If each of the newer turbines has a maximum output power of 16 MW, by how much does the maximum output power of the power station increase?

Q2:

The Three Gorges Dam is a dam of the Yangtze River in China. It is the largest hydroelectric dam in the world, with an installed capacity of 22,500 MW.

The capacity factor of a power plant is the percentage of the installed capacity that is actually supplied to the electricity grid. The capacity factor of the Three Gorges Dam is . What is its actual output power?

Q3:

A hydroelectric dam has 24 identical turbines in it. If the maximum power output of 1 turbine is 18 MW, what is the maximum power output of the whole power station?

Q4:

A lake behind a dam contains 15 km3 of water. The mass of the water is kg. The average height of the water above the river beyond the dam is 60 m. How much gravitational potential energy is stored in the lake?

• A J
• B J
• C J
• D J
• E J

Q5:

Which of the following statements correctly describe the disadvantages of building a hydroelectric dam?

1. Flooding the valley behind the dam submerges the plant life growing there. The plant life dies, and as it rots underwater, it releases large quantities of methane and carbon dioxide. Both of these gases contribute to the greenhouse effect in the atmosphere.
2. Hydroelectric dams are slow to respond to changes in electricity demand.
3. Hydroelectric dams are expensive to build.
4. The running costs of a hydroelectric dam are high.
5. A large amount of concrete is used to build hydroelectric dams. The production of concrete produces a large amount of carbon dioxide that is released into the atmosphere, contributing to climate change.
6. Flooding the valley behind the dam can lead to the loss of habitat for some plant and animal species.
• Aa, c, e, f
• Bb, c, d
• Ca, c, d, f
• Da, b, c, f
• Ed, e, f

Q6:

Which of the following statements correctly describe the advantages of building a hydroelectric dam?

1. Building a hydroelectric dam releases no carbon dioxide into the atmosphere.
2. Building a hydroelectric dam releases no methane into the atmosphere.
3. Hydroelectric dams can respond quickly to changes in energy demand.
4. Hydroelectric dams are very cheap to build.
5. The running costs of a hydroelectric dam are very low.
• Ba, e
• Cb, c
• Dc, e
• Ec, d

Q7:

What type of electric current do the turbines in a hydroelectric dam produce?

• APulsating current
• BDirect current
• CAlternating current
• DRectified alternating current

Q8:

A lake behind a dam contains m3 of water. The average height of the water above the river beyond the dam is 80 m.

What is the mass of the water stored in the lake? Use a value of 1,000 kg/m3 for the density of water.

• A kg
• B kg
• C kg
• D kg
• E kg

How much gravitational potential energy is stored by the water in the lake? Give your answer in joules.

• A J
• B J
• C J
• D J
• E J

of the water in the lake is allowed to pass through hydroelectric turbines in the dam. If this water passes through the turbines at a rate of 40 m3/s, how long will it take this amount of water to pass through the dam? Give your answer in days, to the nearest day.

Q9:

Fill in the blanks: A hydroelectric dam converts energy into energy.

• Agravitational potential, electrical
• Bchemical, electrical
• Ckinetic, chemical
• Dchemical, kinetic
• Egravitational potential, chemical

Q10:

The Hoover Dam is a concrete arch-gravity dam of the Colorado River on the border of Nevada and Arizona. Water from the lake behind the dam is used to drive hydroelectric turbines. The different turbines installed at the Hoover Dam Power Station are listed in the table.

 Turbine Output Power (MW) Number of Turbines Installed 130 127 68.5 61.5 2.4 13 2 1 1 2

What is the total installed capacity of the Hoover Dam Power Station?

The Hoover Dam Power Station has a capacity factor of 23%. If the power station runs continuously for a period of time, what is its actual output power during that period? Give your answer to the nearest megawatt.

What is the total energy output of the Hoover Dam Power Station over the course of a year? Use a value of 365 for the number of days in a year. Give your answer in terawatt-hours to 1 decimal place.

What is the total annual energy output of the Hoover Dam Power Station in petajoules? Give your answer to 1 decimal place. one petajoule is equal to J.

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